Figure-ground

Sorry about the quality of this image taken quickly on the move. It's a rare example of figure-ground problem in action. Perhaps you got it straight away but it took a little while for me to see the image here. I can't think why in retrospect - but, of course, once you've recognised something it's almost impossible to erase your understanding. That's why we need to test icons - the designer knows what they mean, and can never see them fresh.